Reading apparatus and image forming system, and image forming apparatus

ABSTRACT

A reading apparatus includes: a conveyor that conveys transfer paper on which an image has been formed by using rotation of a stepping motor; a driver that performs control in such a manner as to supply control pulses to the stepping motor and rotate the stepping motor in predetermined target rotation steps; an encoder that detects the rotation of the stepping motor and obtains detected rotation steps; a reader that reads the image formed on the transfer paper in a state where the transfer paper is being conveyed by the conveyor; and a controller that detects a difference between an ideal value and an actual value of the detected rotation steps in the target rotation steps, and determines, on the basis of the difference, whether a read in the reader is valid or invalid.

Japanese Patent Application No. 2016-203580 filed on Oct. 17, 2016,including description, claims, drawings, and abstract the entiredisclosure is incorporated herein by reference in its entirety.

BACKGROUND Technological Field

The present invention relates to a technology for appropriately readinga formed image of a chart and adjusting an image forming apparatus.

Description of the Related Art

There is an image forming system where a reading apparatus (an outputmatter reading apparatus) is connected to downstream of an image formingapparatus that forms an image on transfer paper to read the image formedon the transfer paper with the reading apparatus. There is similarly animage forming apparatus in which a reading unit (a scanner=an outputmatter reading unit) is placed downstream of an image forming unit thatforms an image on transfer paper to read the image formed on thetransfer paper with the reading unit.

An image forming apparatus such as a printer or multi-function printerhas an image adjustment mode, and conventionally has the function of, inimage adjustment mode, printing a colorimetric patch of a color,detecting the colorimetric patch with an RGB color density sensor or thelike, comparing the colorimetric patch with print base data, and ifthere is a difference between them, correcting print density and thelike, and forming an image, to increase the quality of an output image.

In recent years, as such an image adjustment mode, there has been animage forming system that reads an image with a scanner while conveyingtransfer paper conveyed after the image was formed to a post processor,analyzes the image data, applies corrections with an image processingapparatus, and provides a stable image. In recent years, an imagereading apparatus where an image scanner is mounted in line in ordownstream of an image forming apparatus to reduce image adjustment timerequired to increase quality has also emerged. The image scanner can beused to correct misalignment on the front and back sides of paper, imagedensity, color, and the like of an output image in real time.

Conveyance upon reading an image on transfer paper requires highaccuracy by using a stepping motor and the like. For example, if theconveying speed is reduced, an incorrect read result that the density ishigher than intended is obtained. On the other hand, if the conveyingspeed is increased, an incorrect read result that the density is lowerthan intended is obtained.

As this type of technology, various related proposals have been made inJP 2007-232986 A.

In JP 2007-232986 A, a stepping motor is used as a drive source,rotational unevenness per revolution is calculated from the number ofoutput pulses of an encoder that detects the angular velocity of arotating body that rotates via a drive gear to create a profile, andchange the stepping motor drive frequency, and accordingly the speed ofthe rotating body is made highly accurate and stable.

Moreover, for example, the detection of stepping motor pull-out is alsoemployed as a known technology. However, it is not possible to handlesubtle speed fluctuations.

However, upon the above conveyance of transfer paper to read an image,the speed may fluctuate suddenly at impact resulting from, for example,a collision of the transfer paper with a conveying roller. Moreover, inan image forming system where a post processing apparatus is connecteddownstream of a reading unit, there are various types of postprocessing. However, load fluctuates during post processing operation.Accordingly, the speed may fluctuate suddenly. Conditions on the sizeand type of transfer paper at post processing, the number of sheets ofpaper to be post processed, and the like vary. It is difficult to applycorrections assuming speed fluctuations. Hence, even if transfer paperis conveyed with high accuracy, when the above speed fluctuations occur,a trouble may occur in image read data. As a result, an image may not beappropriately corrected.

SUMMARY

An object of the present invention is to realize a reading apparatus andan image forming system, and an image forming apparatus that canappropriately correct an image when the speed fluctuates during highlyaccurate conveyance for reading transfer paper.

To achieve the abovementioned object, according to an aspect of thepresent invention, a reading apparatus reflecting one aspect of thepresent invention comprises: a conveyor that conveys transfer paper onwhich an image has been formed by using rotation of a stepping motor; adriver that performs control in such a manner as to supply controlpulses to the stepping motor and rotate the stepping motor inpredetermined target rotation steps; an encoder that detects therotation of the stepping motor and obtains detected rotation steps; areader that reads the image formed on the transfer paper in a statewhere the transfer paper is being conveyed by the conveyor; and acontroller that detects a difference between an ideal value and anactual value of the detected rotation steps in the target rotationsteps, and determines, on the basis of the difference, whether a read inthe reader is valid or invalid.

BRIEF DESCRIPTION OF THE DRAWING

The advantages and features provided by one or more embodiments of theinvention will become more fully understood from the detaileddescription given hereinbelow and the appended drawings which are givenby way of illustration only, and thus are not intended as a definitionof the limits of the present invention:

FIG. 1 is a configuration diagram illustrating a configuration of anembodiment of the present invention;

FIG. 2 is a configuration diagram illustrating a configuration of theembodiment of the present invention;

FIG. 3 is a flowchart illustrating operation of the embodiment of thepresent invention;

FIG. 4 is an explanatory diagram illustrating a state of reading in theembodiment of the present invention;

FIG. 5 is an explanatory diagram illustrating a state of reading in theembodiment of the present invention;

FIG. 6 is a flowchart illustrating operation of the embodiment of thepresent invention;

FIG. 7 is a flowchart illustrating operation of the embodiment of thepresent invention;

FIG. 8 is an explanatory diagram illustrating a state of reading in theembodiment of the present invention;

FIG. 9 is a flowchart illustrating operation of the embodiment of thepresent invention;

FIG. 10 is an explanatory diagram illustrating a state of reading in theembodiment of the present invention;

FIGS. 11A and 11B are explanatory diagrams illustrating a state of motorcontrol in the embodiment of the present invention; and

FIGS. 12A and 12B are explanatory diagrams illustrating a state of motorcontrol in the embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a reading apparatus, an image forming system including thereading apparatus, and an image forming apparatus including the readingapparatus according to one or more embodiments of the present inventionwill be described in detail with reference to the drawings. However, thescope of the invention is not limited to the disclosed embodiments.

[Configuration]

The configuration of the image forming system including the readingapparatus, the image forming apparatus, and a post processing apparatusis described in detail as an example on the basis of FIGS. 1 and 2.

An image forming apparatus 100 is configured including a controller 101that controls units in the image forming apparatus 100, a communicationunit 102 for communicating with another device connected, an operationdisplay unit 103 that accepts a user's operation input and displays astatus of the image forming apparatus 100, a storage unit 104 wherevarious settings are stored, a paper feeder 105 that can feed transferpaper stored on a paper feed tray, a conveyor 110 that conveys transferpaper in the apparatus, a document reader 120 that reads an image of adocument with an imaging device, an image data storage unit 130 whereimage data upon forming an image and various types of data are stored,an image processor 140 that executes various types of image processingrequired to form an image, an image former 150 that forms an image ontransfer paper on the basis of an image formation command and imagedata, and a fixing unit 160 that stabilizes a tonner image formed ontransfer paper, with heat and pressure.

As illustrated in FIG. 2, the image former 150 is configured includingimage carriers on each of which a tonner image is formed, charging unitsthat each charge the image carrier with a predetermined potential,exposing units that each expose the charged image carrier to lightaccording to image data to form a latent image, developing units thateach develop the latent image to change it into a toner image, anintermediate transfer unit on which the toner image of the image carrierof each color is merged, a transfer unit that transfers the toner imageon the intermediate transfer unit onto transfer paper. The image former150 that forms a color image is illustrated here. However, the imageformer may form a single color image.

The controller 101 in the image forming apparatus 100 controls the imageformer 150 in such a manner as to, when having received a notice that aread of an image in a reading apparatus 200 described below is invalid,form the image, the read of which has been determined to be invalid,again on transfer paper. Moreover, the controller 101 in the imageforming apparatus 100 controls the image former 150 in such a manner asto, when having received a notice that a read of an image in the readingapparatus 200 is invalid, if an image is present in an areacorresponding to the notice, form the image being present again in adifferent area on transfer paper. Moreover, the controller 101 in theimage forming apparatus 100 controls the image former 150 in such amanner as to, when having received a notice that a read of an image inthe reading apparatus 200 is invalid, not form an image of an area, theread of which has been determined to be valid, and form an image of anarea, the read of which has been determined to be invalid, again ontransfer paper.

The reading apparatus 200 is placed downstream of the image formingapparatus 100 in a transfer paper travel direction. The readingapparatus 200 is configured including a controller 201, a communicationunit 202, a conveyor 210 that conveys transfer paper, and a reader 220that reads an image formed on transfer paper. It is configured in such amanner that an image on transfer paper formed and output by the imageforming apparatus 100 is read while being conveyed in the readingapparatus 200.

The conveyor 210 is configured including a driver 211, a stepping motor212, an encoder 213, a speed variator 214, and a conveying roller 215.The driver 211 generates control pulses for rotating the stepping motor212 in target rotation steps to convey transfer paper at a predeterminedconveying speed when the transfer paper is read by the reader 220. Theencoder 213 performs detection on a rotary shaft of the stepping motor212, and obtains detected rotation steps. The speed variator 214 changesthe rotational speed of the stepping motor 212 in such a manner that theconveying roller 215 conveys transfer paper at the predeterminedconveying speed.

The controller 201 detects a difference between an ideal value and anactual value of the detected rotation steps of the encoder 213 in thetarget rotation steps of the driver 211, and determines, on the basis ofthe difference, whether a read in the reader 220 is valid or invalid.The controller 201 then notifies the controller 101 of the image formingapparatus 100 of the determination result.

Moreover, the controller 201 controls the target rotation steps of thedriver 211 in such a manner as to offset the above difference.

A post processing apparatus 300 is placed downstream of the readingapparatus 200 in the transfer paper travel direction. The postprocessing apparatus 300 is configured including a controller 301, acommunication unit 302, a conveyor 310 that conveys transfer paper, apost processor 350 that performs post processing such as cutting andfolding on transfer paper, and a discharging unit 390 that dischargestransfer paper. The contents of post processing of the post processor350 are not particularly limited.

The state where the reader 220 is placed in the reading apparatus 200 isillustrated. However, the reader 220 is not limited to this placement,and may be placed, for example, downstream of the fixing unit 160 in theimage forming apparatus 100. In this case, the conveyor 110 controlsconveyance with high accuracy as in the conveyor 210. Moreover, thestate where the reader 220 is placed in the reading apparatus 200 isillustrated. However, the reader 220 is not limited to this placement,and may be placed, for example, upstream of the post processor 350 inthe post processing apparatus 300. In this case, the conveyor 310controls conveyance with high accuracy as in the conveyor 210.

[Operation (1)]

An embodiment of the reading apparatus, a reading control method, and areading control program as operation (1) of the embodiment is describedbelow with reference to a flowchart of FIG. 3. A description is givenhere on the precondition that the image forming apparatus 100 and thereading apparatus 200 work in an interlocked fashion. Moreover, thedescription of the operation is also the processing procedure of thereading control method. Moreover, the description of the operation isalso a description of process steps of the reading control program.

The controller 101 refers to the operating status and past operationrecords of the image forming apparatus 100, and causes the image formingapparatus 100 to operate in measurement mode if needed (step S101 inFIG. 3). Moreover, the controller 201 receives a notice of themeasurement mode from the controller 101, and causes the readingapparatus 200 to operate in measurement mode (step S201 in FIG. 3).

The controller 101 controls the image data storage unit 130 and theimage processor 140 in such a manner as to read a pattern from thestorage unit 104, and generate a chart used in measurement mode, andgenerates chart image data (step S102 in FIG. 3). The controller 101then controls the image former 150 in such a manner as to form an imageof the chart on transfer paper by using the generated chart image data(step S103 in FIG. 3). Moreover, the controller 101 controls theconveyor 110 in such a manner as to convey the chart formed on thetransfer paper to the reading apparatus 200 (step S104 in FIG. 3).

The chart includes crossmarks for registration, and various densitypatches predetermined for each color used in image formation. The chartis, for example, one described in FIG. 4. A state is illustrated inwhich different density patches 1 to 9 have been formed for each colorof CMYK used for image formation. In reality it is also possible to formpatches in more detailed levels or repeatedly form a patch with the samedensity.

In the reading apparatus 200, which has received the transfer paper withthe chart thereon from the image forming apparatus 100, the conveyor 210conveys the transfer paper at a constant speed in accordance with thecontrol by the controller 201 (step S202 in FIG. 3).

The conveyor 210 uses the rotation of the stepping motor 212 controlledby the driver 211 in such a manner as to rotate in predetermined targetrotation steps to change the speed with the speed variator 214, thendrive the conveying roller 215, and convey the transfer paper with thechart thereon (step S203 in FIG. 3).

Moreover, the controller 201 controls the reader 220 in such a manner asto read an image of the chart formed on the transfer paper in a statewhere the transfer paper is being conveyed by the conveyor 210 in thismanner (step S204 in FIG. 3).

The encoder 213 performs detection on the rotary shaft of the steppingmotor 212, performs detection for one step of a rotation of the steppingmotor 212 in a plurality of resolution levels, and outputs a detectedvalue as the detected rotation steps. The plurality of levels indicatesstate levels where at least a pull-out state of the stepping motor 212,and a plurality of states less than pull-out can be distinguished.

The controller 201 then detects a difference between the ideal value andthe actual value of the detected rotation steps in the encoder 213 inthe target rotation steps of the driver 211 (step S205 in FIG. 3). Thecontroller 201 then determines, on the basis of the difference, whethera read in the reader 220 is valid or invalid (step S206 in FIG. 3).

For example, a case is assumed in which when the driver 211 rotates thestepping motor 212 by one step, if the stepping motor 212 rotatesideally without a lead or lag, the encoder 213 outputs 100 pulses as theideal value of the detected rotation steps.

In this case, if the actual value of the detected rotation steps of thestepping motor 212 has a difference equal to or greater than 50 pulsescorresponding to ½ of one step from the ideal value, that is, if theactual value of the detected rotation steps of the encoder 213 is lessthan 49 pulses, or equal to or greater than 151 pulses, the controller201 determines that the stepping motor 212 is under pull-out conditions.In this case, the controller 201 determines that the image of the chartread from the transfer paper conveyed under pull-out conditions isinvalid (step S206 in FIG. 3).

Moreover, if a difference equal to or greater than 10 pulsescorresponding to 1/10 of one step of the stepping motor 212 arisesbetween the ideal value and the actual value, that is, if the actualvalue of the detected rotation steps of the encoder 213 is equal to orless than 90 pulses, or equal to or greater than 110 pulses, thecontroller 201 determines that the stepping motor 212 is not underpull-out conditions but the speed is fluctuating. In this case, thecontroller 201 determines that the image of the chart read from thetransfer paper conveyed in the state where the speed is fluctuating isinvalid (step S206 in FIG. 3).

If a difference less than 10 pulses corresponding to 1/10 of one step ofthe stepping motor 212 arises between the ideal value and the actualvalue, that is, if the actual value of the detected rotation steps ofthe encoder 213 is equal to or greater than 91 pulses and equal to orless than 109 pulses, the controller 201 determines that the conveyingspeed by the stepping motor 212 is within a normal range. In this case,the controller 201 determines that the image of the chart read from thetransfer paper conveyed in the state where the speed is within thenormal range is valid (step S206 in FIG. 3).

The detected rotation steps of the encoder 213 takes any value accordingto the specifications of the encoder 213. Moreover, ½ and 1/10 being thethresholds of a difference between the ideal value and the actual valueof the detected rotation steps may be predetermined as the thresholdsand stored in the storage unit 104. Moreover, the user may change thethresholds if needed.

The controller 201 then notifies the controller 101 of the image formingapparatus 100 via the communication units 202 and 102 of a determinationresult (read image=invalid or read image=valid) based on a differencebetween the ideal value and the actual value of the detected rotationsteps as described above (steps S207, S208, and S209 in FIG. 3).

Moreover, the controller 201 transmits the read image data obtained byreading the chart with the reading apparatus 200 to the controller 101of the image forming apparatus 100 via the communication units 202 and102 (step S210 in FIG. 3).

The controller 101, which has received a determination result ofvalidity/invalidity of a read image as described above (step S105 inFIG. 3), controls the image data storage unit 130 and the imageprocessor 140 in such a manner as to, if the read image had beendetermined to be invalid (NO in step S106 in FIG. 3), read a patternfrom the storage unit 104 for an image of the same chart as the onewhose read image data had been determined to be invalid, and generate achart used in measurement mode, and generates chart image data (stepS107 in FIG. 3). The controller 101 then performs control in such amanner as to again repeat the formation of an image of the generatedchart image data on transfer paper (step S103 in FIG. 3) and theconveyance of the chart formed on the transfer paper to the readingapparatus 200 (step S104 in FIG. 3).

On the other hand, the controller 101, which has received adetermination result of validity/invalidity of a read image as describedabove (step S105 in FIG. 3), if the read image was determined to bevalid (YES in step S106 in FIG. 3), makes various image adjustments to,for example, density and the image forming position, in the image former150, by using the read image data of the chart (step S108 in FIG. 3).

The controller 101 then controls the image data storage unit 130 and theimage processor 140 in such a manner as to read a pattern from thestorage unit 104 for an image of the next chart and generate a chartused in measurement mode, and generates chart image data to form imagesof charts of the number of sheets required in measurement mode (NO instep S109 and S110 in FIG. 3). The controller 101 then performs controlin such a manner as to again repeat the formation of an image of thegenerated next chart image data on transfer paper (step S103 in FIG. 3)and the conveyance of the chart formed on the transfer paper to thereading apparatus 200 (step S104 in FIG. 3). In response to this, thecontroller 201 controls the units of the reading apparatus 200 in such amanner as to repeat a read of a chart and a determination based on adifference between the ideal value and the actual value of the detectedrotation steps.

If having completed the formation of images of charts of the number ofsheets required in measurement mode and adjustments based on read imagedata (YES in step S109 in FIG. 3), then the controller 101 transmits acompletion notice to the controller 201 via the communication units 102and 202 (step S111 in FIG. 3), and ends the processing in measurementmode (END in FIG. 3). Similarly the controller 201, which has receivedthe completion notice, also ends the processing in measurement mode (YESin step S211 and END in FIG. 3).

FIG. 4 illustrates a state where read image data of a chart whose imagewas formed has been determined to be valid without influence of speedfluctuations on a read.

On the other hand, FIG. 5 illustrates by example a case where thecontroller 201 has determined that a read (FIG. 5(b 1)) of a chart whoseimage was formed (FIG. 5(a 1)) is invalid due to a speed abnormality inarea #3. In this case, the controller 101 controls the image former 150in such a manner as to again form the image of the chart which wasformed (FIG. 5(a 1)) (steps S208 and S107 in FIG. 3). Consequently, evenif the speed fluctuates during highly accurate conveyance for readingtransfer paper, an image of the same chart is formed again and read.Accordingly, valid read image data can be obtained to enable appropriateimage corrections.

It may be configured in such a manner that an image of not the entirechart but only an area that has been determined to be invalid is formedand read when the image of the same chart is formed again in FIG. 5(a2).

This area may be determined on the basis of a separation position of apatch in a sub-scanning direction by obtaining information on the patchfrom the image forming apparatus 100, or an area may be predeterminedregardless of the position of the patch.

[Operation (2)]

An embodiment of the reading apparatus, the reading control method, andthe reading control program as operation (2) of the embodiment isdescribed below with reference to a flowchart of FIG. 6. An overlappingdescription of the same processes as the already described operation (1)is omitted here.

The controller 101, which has received a determination result ofvalidity/invalidity of a read image from the controller 201 as describedabove (step S105 in FIG. 6), if the read image was determined to beinvalid (NO in step S106 a in FIG. 6), determines whether or not theinvalidity determination influences adjustments (step S106 b in FIG. 6).The invalidity determination of the controller 201 may be relaxed in,for example, an adjustment to be made (NO in step S106 b in FIG. 6). Thecontroller 101 similarly handles this case to a case where a read imageis determined to be valid (NO in step S106 b in FIG. 6) to make variousimage adjustments to, for example, density and the image formingposition, in the image former 150 by using the read image data of thechart (step S108 in FIG. 6).

On the other hand, after the controller 201 determined that the readimage is invalid (NO in step S106 a in FIG. 3), if the controller 101has determined that the invalidity determination influences theadjustments (YES in step S106 b in FIG. 6), the controller 101 controlsthe image data storage unit 130 and the image processor 140 in such amanner as to read a pattern from the storage unit 104 for an image ofthe same chart as the one whose read image data has been determined tobe invalid, and generate a chart used in measurement mode, and generateschart image data (step S107 in FIG. 3). The controller 101 then performscontrol in such a manner as to again repeat the formation of an image ofthe generated chart image data on transfer paper (step S103 in FIG. 3),and the conveyance of the chart formed on the transfer paper to thereading apparatus 200 (step S104 in FIG. 3).

In the above case, also if an area that has been determined by thecontroller 201 that a read is invalid is an area where a patch of thechart is not present, there is no adverse effect on the read image data(NO in step S106 b in FIG. 6). The controller 101 similarly handles thiscase to the case where a read image is determined to be valid (NO instep S106 b in FIG. 6), and makes various image adjustments to, forexample, density and the image forming position, in the image former 150by using the read image data of the chart (step S108 in FIG. 6).

[Operation (3)]

An embodiment of the reading apparatus, the reading control method, andthe reading control program as operation (3) of the embodiment isdescribed below with reference to a flowchart of FIG. 7. An overlappingdescription of the same processes as the already described operation (1)and (2) is omitted here.

The controller 101, which has received a determination result ofvalidity/invalidity of a read image from the controller 201 as describedabove (step S105 in FIG. 7), if the read image has been determined to beinvalid (NO in step S106 in FIG. 7), controls the image former 150 insuch a manner as to read a pattern from the storage unit 104 for animage of the same chart as the one whose read image data has beendetermined to be invalid and again form an image of an area determinedto be invalid in an area different from the original area on transferpaper (step S107′ in FIG. 7).

The different area in this case indicates an area that is different atleast in the sub-scanning direction to handle speed fluctuationsresulting from vibrations related to the conveyance. Moreover, in orderto again form the image of the area determined to be invalid in the areadifferent from the original area on the transfer paper, an image of anarea determined to be valid is not formed to create a blank area.

In other words, if an image is present in an area determined to beinvalid, the image present is formed again in a different area ontransfer paper. Accordingly, the possibility to be able to avoidrepeatable speed fluctuations is increased. When the speed fluctuatesduring highly accurate conveyance for reading transfer paper, it becomespossible to make appropriate image corrections.

Assume that a speed fluctuation has been detected in area #3 in thereading apparatus 200 (refer to FIG. 8(b 1)). In this case, thecontroller 101 is configured to form an image of an area determined tobe invalid in an area other than area #3, for example, area #2 (FIG. 8(a2)), and read the chart in the reading apparatus 200 (FIG. 8(b 2)).Consequently, the possibility to be able to avoid speed fluctuationsresulting from, for example, entry into between rollers upon conveyanceis increased. If the speed fluctuates during highly accurate conveyancefor reading transfer paper, it becomes possible to make appropriateimage corrections.

Moreover, in order to prevent a read of the chart whose image has beenformed again from being determined again to be invalid, it is alsopossible to form the image originally formed in area #3 in a pluralityof areas #2 and #4.

[Operation (4)]

An embodiment of the reading apparatus, the reading control method, andthe reading control program as operation (4) of the embodiment isdescribed below with reference to a flowchart of FIG. 9. An overlappingdescription of the same processes as the already described operation(1), (2), and (3) is omitted here.

When a notice of an area where a read of an image was determined to beinvalid has been received as described above (step S105 in FIG. 9),there is a plurality of sheets of transfer paper each including an areawhere a read was determined to be invalid, a chart where images of aplurality of the areas, where a read was determined to be invalid, onthe plurality of sheets of transfer paper are collected is generated(step S107″ in FIG. 9).

Assume, in FIG. 10, that a speed fluctuation was detected in area #3 ona first sheet (refer to FIG. 10(b 1)), and then in area #4 on a secondsheet (refer to FIG. 10(b 2)) in the reading apparatus 200. A pluralityof areas of the charts determined to be invalid is collected in onechart (FIG. 10(a 3)) in this manner to form an image on transfer paper.Accordingly, it becomes possible to form and read an image of the chartwithout waste, and to make appropriate image corrections if the speedfluctuates during highly accurate conveyance for reading transfer paper.In this case, it also becomes possible to avoid waste of transfer paperand reduce the measurement time.

[Operation (5)]

In the above operation, the controller 201 is desired to control thepulse width of the target rotation steps of the driver 211 in real time,or after acquiring a difference pattern, to offset the above difference.

Assume, for example, that differences are accumulated as in FIG. 11A. Inthis case, the controller 201 acquires a pattern of the accumulation ofthe differences. As in FIG. 11B, the driver 211 then controls the pulsewidth of steps supplied to the stepping motor 212 to bring thecumulative difference to zero. It is simply required to perform controlwith, for example, the number of clock pulses that determines the pulsewidth. In FIG. 11B, the number of clock pulses that determines the pulsewidth of the target rotation steps in the driver 211 is changed to 2999or 3001 as compared with a target of 3000.

As a result, such cumulative differences before correction asillustrated in FIG. 12A are controlled in such a manner as to be broughtto zero by offsetting the differences as in FIG. 12B. Hence, theconveying speed of transfer paper can be kept constant with higheraccuracy. If the speed fluctuates during highly accurate conveyance forreading transfer paper, it becomes possible to make appropriate imagecorrections.

Moreover, the example where a difference pattern is acquired wasillustrated here. However, if the encoder 213 detects a difference inreal time, the driver 211 may control the pulse width of the next stepsupplied to the stepping motor 212.

(1) According to an embodiment of the invention, in a reading apparatusreflecting one aspect of the present invention, transfer paper on whichan image has been formed is conveyed by using rotation of a steppingmotor controlled in such a manner as to be rotated in predeterminedtarget rotation steps, a reader reads the image formed on the transferpaper in a state where the transfer paper is being conveyed by aconveyor, an encoder detects detected rotation steps of the steppingmotor, and a controller determines whether a read in the reader is validor invalid on the basis of a difference between an ideal value and anactual value of the detected rotation steps. Consequently, if thedifference between the detected rotation steps and the target rotationsteps is equal to or greater than a constant value, the read isdetermined to be invalid. If the difference between the detectedrotation steps and the target rotation steps is less than the constantvalue, the read is determined to be valid. Accordingly, it becomespossible to make appropriate image corrections if the speed fluctuatesduring highly accurate conveyance for reading transfer paper.

(2) In the above reading apparatus of (1), the controller determinesthat the read in the reader is invalid if the difference exceeds apredetermined threshold on the basis of a comparison of the differenceand the threshold. Consequently, validity or invalidity of a read iscorrectly determined. Accordingly, it becomes possible to makeappropriate image corrections if the speed fluctuates during highlyaccurate conveyance for reading transfer paper.

(3) In the above reading apparatus of (1) and (2), the transfer paper isdivided into a plurality of areas to determine whether the read in thereader is valid or invalid. Consequently, an invalid area is not usedfor correction, and a valid area is used for correction. Accordingly, itbecomes possible to make appropriate image corrections if the speedfluctuates during highly accurate conveyance for reading transfer paper.

(4) In the above reading apparatus of (1) to (3), the encoder is placedin such a manner as to perform detection on a rotary shaft of thestepping motor. Consequently, the detected rotation steps can bedetected directly from the stepping motor without being influenced byspeed fluctuations caused by a speed variation mechanism, theaccommodation of the fluctuations, and the like. Accordingly, it becomespossible to make appropriate image corrections if the speed fluctuatesduring highly accurate conveyance for reading transfer paper.

(5) In the above reading apparatus of (1) to (4), the controllercontrols the target rotation steps of a driver in such a manner as tooffset the difference. Consequently, the conveying speed of transferpaper can be kept constant with high accuracy. Accordingly, it becomespossible to make appropriate image corrections if the speed fluctuatesduring highly accurate conveyance for reading transfer paper.

(6) In an image forming system reflecting one aspect of the presentinvention, transfer paper on which an image has been formed is conveyedby using rotation of a stepping motor controlled in such a manner as tobe rotated in predetermined target rotation steps, a reader reads theimage formed on the transfer paper in a state where the transfer paperis being conveyed by a conveyor, an encoder detects detected rotationsteps of the stepping motor, and a controller determines whether a readin the reader is valid or invalid on the basis of a difference betweenan ideal value and an actual value of the detected rotation steps in thetarget rotation steps. Consequently, if the difference between thedetected rotation steps and the target rotation steps is equal to orgreater than a constant value, the read is determined to be invalid. Ifthe difference between the detected rotation steps and the targetrotation steps is less than the constant value, the read is determinedto be valid. Accordingly, it becomes possible to make appropriate imagecorrections if the speed fluctuates during highly accurate conveyancefor reading transfer paper.

(7) In the above image forming system of (6), an image formingapparatus, which has received a notice that the read of the image in thereading apparatus is invalid, forms the image where the read has beendetermined to be invalid, again on transfer paper. Accordingly, itbecomes possible to make appropriate image corrections if the speedfluctuates during highly accurate conveyance for reading transfer paper.

(8) In the above image forming system of (6), an image formingapparatus, which has received a notice that the read of the image in thereading apparatus is invalid, when an image is present in an areacorresponding to the notice, forms the image present again in adifferent area on transfer paper. Accordingly, the possibility to beable to avoid repeatable speed fluctuations is increased, and it becomespossible to make appropriate image corrections if the speed fluctuatesduring highly accurate conveyance for reading transfer paper.

(9) In the above image forming system of (6) to (8), the image formingapparatus, which has received a notice that the read of the image in thereading apparatus is invalid, does not form an image of an area wherethe read has been determined to be valid, and forms an image of an areawhere the read has been determined to be invalid, again on transferpaper. Accordingly, it becomes possible to perform a read in a statewithout waste, and to make appropriate image corrections if the speedfluctuates during highly accurate conveyance for reading transfer paper.

(10) In the above image forming system of (6) to (9), the image formingapparatus, which has received a notice of an area where a read of animage in the reading apparatus is invalid, when a plurality of areaswhere a read was determined to be invalid is present, forms an image ontransfer paper in a state where images of the plurality of areas wherethe read was determined to be invalid has been collected. Accordingly,it becomes possible to perform a read in a state without waste and tomake appropriate image corrections if the speed fluctuates during highlyaccurate conveyance for reading transfer paper.

(11) In an image forming apparatus reflecting one aspect of the presentinvention, transfer paper on which an image has been formed is conveyedby using rotation of a stepping motor controlled in such a manner as tobe rotated in predetermined target rotation steps, a reader reads theimage formed on the transfer paper in a state where the transfer paperis being conveyed by a conveyor, an encoder detects detected rotationsteps of the stepping motor, and a controller determines whether a readin the reader is valid or invalid on the basis of a difference betweenan ideal value and an actual value of the detected rotation steps in thetarget rotation steps. Consequently, if the difference between thedetected rotation steps and the target rotation steps is equal to orgreater than a constant value, the read is determined to be invalid. Ifthe difference between the detected rotation steps and the targetrotation steps is less than the constant value, the read is determinedto be valid. Accordingly, it becomes possible to make appropriate imagecorrections if the speed fluctuates during highly accurate conveyancefor reading transfer paper.

(12) In the above image forming apparatus of (11), if a notice that theread of the image in the reading apparatus is invalid has been received,when an image is present in an area corresponding to the notice, theimage present is formed again in a different area on transfer paper.Accordingly, the possibility to be able to avoid repeatable speedfluctuations is increased, and it becomes possible to make appropriateimage corrections if the speed fluctuates during highly accurateconveyance for reading transfer paper.

(13) In the above image forming apparatus of (11) and (12), if a noticethat the read of the image in the reading apparatus is invalid has beenreceived, an image of an area where the read has been determined to bevalid is not formed, and an image of an area where the read has beendetermined to be invalid is formed again on transfer paper. Accordingly,it becomes possible to perform a read in a state without waste and tomake appropriate image corrections if the speed fluctuates during highlyaccurate conveyance for reading transfer paper.

(14) In the above image forming apparatus of (11) to (13), if a noticeof an area where a read of an image in the reading apparatus is invalidhas been received, and a plurality of areas where a read was determinedto be invalid is present, an image is formed on transfer paper in astate where images of the plurality of areas where the read wasdetermined to be invalid has been collected. Accordingly, it becomespossible to form and read an image of a chart in a state without wasteand to make appropriate image corrections if the speed fluctuates duringhighly accurate conveyance for reading transfer paper.

Although embodiments of the present invention have been described andillustrated in detail, it is clearly understood that the same is by wayof illustration and example only and not limitation, the scope of thepresent invention should be interpreted by terms of the appended claims.

What is claimed is:
 1. A reading apparatus comprising: a conveyor thatconveys transfer paper on which an image has been formed by usingrotation of a stepping motor; a driver that performs control in such amanner as to supply control pulses to the stepping motor and rotate thestepping motor in predetermined target rotation steps; an encoder thatdetects the rotation of the stepping motor and obtains detected rotationsteps; a reader that reads the image formed on the transfer paper in astate where the transfer paper is being conveyed by the conveyor; and acontroller that detects a difference between an ideal value and anactual value of the detected rotation steps in the target rotationsteps, and determines, on the basis of the difference, whether a read inthe reader is valid or invalid.
 2. The reading apparatus according toclaim 1, wherein the controller determines that the read in the readeris invalid upon the difference exceeding a predetermined threshold onthe basis of a comparison of the difference and the threshold.
 3. Thereading apparatus according to claim 1, wherein the reader reads thedensity or color of the image formed on the transfer paper, and thecontroller divides the transfer paper into a plurality of areas todetermine, on the basis of the difference, whether the read in thereader is valid or invalid.
 4. The reading apparatus according to claim1, wherein the encoder is placed in such a manner as to performdetection on a rotary shaft of the stepping motor.
 5. The readingapparatus according to claim 1, wherein the controller controls thetarget rotation steps of the driver in such a manner as to offset thedifference.
 6. An image forming system comprising: an image formingapparatus that forms an image on transfer paper; and the readingapparatus according to claim 1, that reads the image formed by the imageforming apparatus on the transfer paper, wherein the reading apparatusnotifies the image forming apparatus of a result of a determination onwhether the read is valid or invalid.
 7. The image forming systemaccording to claim 6, wherein upon having received a notice that theread of the image in the reading apparatus is invalid, the image formingapparatus forms the image where the read has been determined to beinvalid, again on transfer paper.
 8. The image forming system accordingto claim 6, wherein upon having received a notice that the read of theimage in the reading apparatus is invalid, when an image is present inan area corresponding to the notice, the image forming apparatus formsthe image present again in a different area on transfer paper.
 9. Theimage forming system according to claim 6, wherein upon having receiveda notice that the read of the image in the reading apparatus is invalid,an image of an area where the read has been determined to be valid isnot formed, and an image of an area where the read has been determinedto be invalid is formed again on transfer paper.
 10. The image formingsystem according to claim 6, wherein upon having received a notice of anarea where a read of an image in the reading apparatus is invalid, and aplurality of areas where a read was determined to be invalid beingpresent, the image forming apparatus forms an image on transfer paper ina state where images of the plurality of areas where the read wasdetermined to be invalid have been collected.
 11. An image formingapparatus comprising: an image former that forms an image on transferpaper; the reading apparatus according to claim 1, that reads the imageformed by the image former on the transfer paper; and a controller thatcontrols formation and reading of the image, wherein upon havingreceived a notice that the read of the image in the reading apparatus isinvalid, the controller controls the image former to form the imagewhere the read has been determined to be invalid, again on transferpaper.
 12. The image forming apparatus according to claim 11, whereinupon having received a notice that the read of the image in the readingapparatus is invalid, when an image is present in an area correspondingto the notice, the controller controls the image former in such a manneras to form the image present again in a different area on transferpaper.
 13. The image forming apparatus according to claim 11, whereinupon having received a notice that the read of the image in the readingapparatus is invalid, the controller controls the image former in such amanner as to not form an image of an area where the read has beendetermined to be valid, and form an image of an area where the read hasbeen determined to be invalid, again on transfer paper.
 14. The imageforming apparatus according to claim 11, wherein upon having received anotice of an area where a read of an image in the reading apparatus isinvalid, and a plurality of areas where a read was determined to beinvalid being present, the controller controls the image former in sucha manner as to form an image on transfer paper in a state where imagesof the plurality of areas where the read was determined to be invalidhave been collected.